Timer for an appliance

ABSTRACT

A timer includes a bank of switching means, a bank of impedance means, means coupling at least one of the switching means to at least one of the impedance means, and capacitor means connected in series to the bank of impedance means.

[ TIMER FOR AN APPLIANCE [75] Inventor: Philip L. Schmidgall, Indianapolis,

Ind.

[73] Assignee: P. R. Mallory & Co. Inc.,

Indianapolis, Ind.

221 Filed: 1111 .11, 1971 21 Appl. No.: 170,816

[52] US. Cl 307/133, 307/141, 219/395 [51] Int. Cl. H0lh 7/00 [58] Field of Search 307/14l.8, 141.4,

[ 1 Oct. 23, 1973 3,553,483 12/1968 Jarvis 307/141 Primary ExaminerHerman J. Hohauser Attorney-Richard H. Childress et a1.

[57] ABSTRACT A timer includes a bank of switching means, a bank of impedance means, means coupling at least one of the switching means to at least one of the impedance means, and capacitor means connected in series to the [56]- Reterences Cited bank of impedance means.

UNITED STATES PATENTS 3,397,323 8/1968 Hirsch 307/141 12 Claims, 2 Drawing Figures i T T T T T T T T T T T I0 I j I SWlTCHlN l POWER POWER MEANS POWER I l SWITCHING SUPPLY TURNOFF l I MEANS MEANS T|M|NG MEANS l I 1 :2 14 MEANS l6 l RELAY MEANS 22 SAFETY APPLIANCE SHUT-OFF MEANS 2O 24 PAIENIEB 0C! 2 3 I818 POWER TURN-OFF MEANS MEANS I. I SWITCHING TIMING MEANS POWER SUPPLY MEANS POWER SWITCH l NG MEANS SAFETY SHUT-OFF MEANS RELAY MEANS \22 APPLIANCE 1 TIMER FOR AN APPLIANCE This invention relates to a timer; and more particularly to a timer which'operates an appliance for a predetermined period of time.

Appliances, such as microwave ovens, are being increasingly used in places such as restaurants and cafeterias to heat cold foods purchased by the customer. After purchasing the cold food, the customer puts the food into the oven and then pushes a button which will cause a timer to operate to allow heat to be applied to the food for a certain period of time. The button selected determines the length of time which the food will be heated.

One method of providing for the desired time intervals in such an application would be to use a potentiometer adjustment. However, such a system may take several adjustments to get the desired timing intervals, thereby rendering the system time consuming.

The present invention is concerned with a timer which is particularly adaptable to operating an appliance for a predetermined period of time which may be selected by an operator and has as an object the provision of-such a timer which provides for selection of the time interval in one easy operation.

Another object of the invention is the provision of a timer having a means for selecting a time interval for heating a microwave oven for predetermined periods of time.

Still another object of the invention is the provision of the timer having a bank of impedance means, a bank of switching means, and means selectively coupling at least one of the switching means to the impedance means.

Still another object of the invention is the provision of a timer, the time interval of which is determined by a bank of impedance means in series with a capacitance means.

Yet still another object of the invention is the provisionof a timer having a power switching means, a power supply meansre'sponsive to the power switching means, timing means responsive to the power supply means, and power turn off means which is responsive to the timing means to selectively de-energize the power switching means.

Another object of the invention is the provision of the combination of an appliance operable for a predetermined length of time and a timer providing the predetermined length of time, the timer including a bank of switch means, a bank of impedance means, and means selectively coupling at least one of the switch means to at least one of the impedance means, and a capacitor means in series with the bank of impedance means.

These and other objects of the invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram showing the elements of the timer in combination with an appliance; and

FIG. 2 is a wiring diagram showing the timer of the present invention.

Generally speaking, the objects of the invention are accomplished by providing a timer comprising power switching means, power supply means responsive to the power switching means, timing means responsive to the power supply means, and power turn-off means responsive to the timing means to selectively de-energize the power switching means. The timing means includes a bank of switching means, a bank of impedance means, means coupling at least one of the switching means to at least one of the impedance means, and capacitor means connected in series to the bank of impedance means. When used in combination with an appliance such as a microwave oven, the coupling of the switching means with the impedance means determines the length of time during which the appliance will be operable.

Referring now to the drawings, and particularly to FIG. 1, timer 10 includes power switching means 12, power supply means 14, timing means 16, and power tum-off means 18. The timer may, through the power switching means 12, activate an appliance 20, such as a microwave oven, through a relay means 22. As will become apparent, appliance 20 will be operable for a predetermined period of time until the power switching means 12 is de-energized through power turn-off means 18. A safety shut-off means 24 is responsive to a condition of the appliance 20 to activate timing means 16 thereby energizing power turn-off means which de-energizes the timer 10 to shut-off power to the appliance. As shown, activation of power switching means 12 activates power supply means 14 which in turn activates timing means 16, timing means 16 operating power tum-off means 18. As will become apparent with reference to FIG. 2, timing means 16 includes a switching means 26. Although switching means 26 is functionally part of timing means 16 the switching means should be constructed unitarily with power switching means 12. Therefore it is shown in FIG. 1 that switching means 26 is activated when power switching means 12 is activated.

Referring to FIG. 2, the timing means 10 is connected across a suitable power source at lines L L Switching means 12 includes a plurality of switches 12' which may be of the push button type having a double a contact with one of the contacts serving as the power switching means. The other contact serves as the switches 26' of the switching means '26 included as a part of the timing means 16. Power supply means 14 includes a series combination of diode 30, resistor 32, and capacitor 34. The power supply means converts AC current to'DC current which is supplied to the balance of the circuit. Timing means 16 is a relaxation oscillator including timing selector means 36, capacitance means 38. The timing selector means 36 is connected between junctions A and B and includes a bank of impedance means 42 such as a bank of timing resistors 44. The resistors 44 are electricaly connected in A series with male terminal plugs 46 between each resistor. The bank of switches 26' are electricaly coupled to female terminals 48 such that a means 50 may be used to selectively couple the switches to the resistors. Such means could include patch chords used to selectively couple a male terminal to a female terminal. in this manner, various resistance values may be obtained so as to vary the time periods that the timing means will be operable through the various combinations of the capacitor means 38 and the bank of resistors. Capacitor means 38 includes a timing capacitor 38'. Also included as part of the timing means 16 is a programmable unijunction transistor (PUT) 52 and a voltage divider network comprising resistors 54, 56, and 58, resistor 56 being a variable resistor. The gate of the programmable unijunction transistor is connected to the variable resistor 56, its anode is connected to junction B through load resistor 60 and its cathode is connected to the switching means 62 of the power turn-off means 18 and to ground through load resistor 64. The power turn-off means 18 includes solenoid means 66 connected in series with switching means 62. Relay means 66 includes a solenoid 66 while switching means 62 includes an SCR 62' connected anode to the solenoid, cathode to ground, and gate to the relaxation oscillator means 40.

Where it is required for the particular appliance, a safety means may be included as part of the timer circuitry. For example, in a microwave oven, means may beprovided to turn off the power to the complete sys tem when the oven door is opened. As part of the present combination, a safety shut-off means 24 is included as part of the timing means 16; but it is to be understood that it need not be necessarily so included. Safety shut-offmeans 24 includes a suitable switch 70 responsive to a condition of the appliance in series with loa resistor 72. g

In operation, when any one of the number of push buttons (not shown) corresponding to the number of switches 12 or 26' is fully depressed, two switch contacts on the push button close and the push button is latched in the .ON position by aspring loaded latch bar 12" which is connected to solenoid 66'. Contacts for the power switching means 12 control power to external relay 22, power supply means 14 and voltage divider resistors 54, 56, and 58. Contacts for the switch means 26 connect the preselected timing resistor(s) 44 between points A and B. The timing resistor(s) and therefore the time are preselected by connecting coupling means 50, such as a patch chord, from a desired switch terminal 48 to a desired resistor terminal 46. As current flows from junction A through the timing resistor(s) to junction B, the voltage on timing capacitor 38 begins to rise. When the voltage on timing capacitor 38 reaches a voltage slightly higher than the voltage appearing at resistor 56, PUT 52 conducts until the voltage on the timing capacitor 38 (which is now dischargingthrough PUT 52) reaches the same voltage as the junction voltage drop across PUT 52. When PUT 52 conducts through resistor 64, a voltage is generated at the gate of SCR 62 which causes it to conduit. When SCR 62' conducts, current flows through solenoid coil 66' and actuates the latch bar which releases the push button. With the push botton released, both switch contacts open, de-energizing external relay 22 and power supply means 14 thus ending the timing cycle, and shuting off the appliance.

What is claimed is:

l. A timer comprising:

a. power switching means b. power supply means responsive to said power switching means, I 1

c. timing means responsive to said power supply means, and

d. power turn-off means responsive to said timing means to de-energize said power switching means,

e. said timing means including a bank of switching means, a bank of impedance means, a patch chord coupling at least one of said switching means to at least one of said impedance means, and capacitor means connected in series to said bank of impedance means.

2. A timer according to claim 1 wherein said impedance means are resistors. A

3. A timer according to claim 1 wherein said capacitor means is at least one capacitor.

4. A timer according to claim 1 wherein said timing means further includes a relaxation oscillatormeans.

5. A timer according to claim 4 wherein said relaxation oscillator includes a programmable unijunction transistor.

6. A timer according to claim 1' wherein said power turn-off means includes a switching means in series with a relay means.

7. A timer according to claim 6 wherein said switching means includes an SCR and said relay means includes a solenoid. I

8. A timer according to claim 1 wherein said power supply means includes a series combination of a diode, resistor, and capacitor.

9. In combination, an appliance operable for a predetermined length of time and a timer providing said predetermined length of time; said timer including a timing selector means including a bank of switch means, a

bank of impedance means, and a patch chord selectively coupling at least one of said switch means to at least one of said impedance means; and a capacitor means in series with said bank of impedance means; selectively coupling of said switching means with said impedance means providing said predetermined length of time said appliance is operable.

10. The combination according to claim 9 further including safety shut-off means responsive to a condition of said appliance to shut-off said timer.

11. The combination according to claim 10 wherein said safety shut-off means is included in said timing means.

12. The combination according to claim 9'wherein said appliance is operable in response to a relay means responsive to said timer.

UNITED STATES PATENT OFFICE CERTH KQATE OF CORRECTION Patent No. 3 767 ,937 Dated October 23, 1973 Inventor-(s) Phillip L. Schmidgall It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 45, change "conduit" to -conduct.

Signed and sealed this 23rd day of April 1971;.

(SEAL) Attest:

EDWARD PLFLEICHERJR. C. MARSHALL DANN Attesting Officer Commissionerof Patents Patent No. 3, 767 ,937 Dated October 23, 1973 Inventm-(S) Phillip L. Schmidgall It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 45, change "conduit" to ---conduct---.

Signed and sealed this 23rd day of April 1971;.

(SEAL) Attest:

EDWARD TLFLETCTEELJR. C. MARSHALL DANN Attesting Officer- Commissioner of Patents 

1. A timer comprising: a. power switching means b. power supply means responsive to said power switching means, c. timing means responsive to said power supply means, and d. power turn-off means responsive to said timing means to deenergize said power switching means, e. said timing means including a bank of switching means, a bank of impedance means, a patch chord coupling at least one of said switching means to at least one of said impedance means, and capacitor means connected in series to said bank of impedance means.
 2. A timer according to claim 1 wherein said impedance means are resistors.
 3. A timer according to claim 1 wherein said capacitor means is at least one capacitor.
 4. A timer according to claim 1 wherein said timing means further includes a relaxation oscillator means.
 5. A timer according to claim 4 wherein said relaxation oscillator includes a programmable unijunction transistor.
 6. A timer according to claim 1 wherein said power turn-off means includes a switching means in series with a relay means.
 7. A timer according to claim 6 wherein said switching means includes an SCR and said relay means includes a solenoid.
 8. A timer according to claim 1 wherein said power supply means includes a series combination of a diode, resistor, and capacitor.
 9. In combination, an appliance operable for a predetermined length of time and a timer providing said predetermined length of time; said timer including a timing selector means including a bank of switch means, a bank of impedance means, and a patch chord selectively coupling at least one of said switch means to at least one of said impedance means; and a capacitor means in series with said bank of impedance means; selectively coupling of said switching means with said impedance means providing said predetermined length of time said appliance is operable.
 10. The combination according to claim 9 further including safety shut-off means responsive to a condition of said appliance to shut-off said timer.
 11. The combination according to claim 10 wherein said safety shut-off means is included in said timing means.
 12. The combination according to claim 9 wherein said appliance is operable in response to a relay means responsive to said timer. 